Significance

Understanding of the insulator–metal Mott transition in correlated systems has been one of the central themes in condensed-matter physics for more than half a century. The original Mott concept of a transition mechanism has been proposed in terms of the screening of Coulomb potential at high pressures, which, however, has not yet been experimentally validated. Such a scenario, for the first time to our knowledge, is unveiled in multiferroic PbCrO3 with collapse of both the volume and Coulomb potential at high pressures, which is associated with atomic ferroelectric distortion. In addition, Mott critical behaviors, magnetic and ferroelectric properties, and the isostructural phase transition of this material are also explored. Findings in this work are fundamentally and technologically important for the study of correlated systems.

Abstract

The Mott insulator in correlated electron systems arises from classical Coulomb repulsion between carriers to provide a powerful force for electron localization. Turning such an insulator into a metal, the so-called Mott transition, is commonly achieved by “bandwidth” control or “band filling.” However, both mechanisms deviate from the original concept of Mott, which attributes such a transition to the screening of Coulomb potential and associated lattice contraction. Here, we report a pressure-induced isostructural Mott transition in cubic perovskite PbCrO3. At the transition pressure of ∼3 GPa, PbCrO3 exhibits significant collapse in both lattice volume and Coulomb potential. Concurrent with the collapse, it transforms from a hybrid multiferroic insulator to a metal. For the first time to our knowledge, these findings validate the scenario conceived by Mott. Close to the Mott criticality at ∼300 K, fluctuations of the lattice and charge give rise to elastic anomalies and Laudau critical behaviors resembling the classic liquid–gas transition. The anomalously large lattice volume and Coulomb potential in the low-pressure insulating phase are largely associated with the ferroelectric distortion, which is substantially suppressed at high pressures, leading to the first-order phase transition without symmetry breaking.

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